Temperature control system



Feb. 16, L, YOUNG ET AL TEMPERATURE CONTROL SYSTEM Filed Oct. 15, 1931 Dm Y 6 E N mmu N Y .0. L T E I. T M w A 1 JL Patented Feb. 16, 1937UNITED STATES PATENT OFFICE assignors to Radio Corporation of America, acorporation of Delaware Application October 15, 1931, Serial No. 568,962

7 Claims.

This invention relates to a method of, and apparatus for regulating thetemperature of frequency control devices, and has especial reference toapparatus for controlling the temperature of a pieZo-electric crystalresonator.

One or" the objects of the present invention is to provide an improvedmethod of controlling the frequency of a piezo-electric crystalresonator.

Piezo-electric crystals are frequently employed in radio signaltransmitters for controlling the frequency of high frequencyoscillators. It has been found that these crystals, in order to functionproperly, must be maintained at substantially constant temperature.Heretofore it has been customary in order to control the temperature ofthe piezo-electric crystal to enclose the crystal in a receptacle and toregulate the temperature of the air within the container. In such case,the heat liberated by the crystal resonator while Vibrating is conductedto the walls of the receptacle through the medium of the air within thecontainer. Since air is a poor conductor of heat it has been found thatthe crystal, frequently, is at a much higher temperature than thereceptacle. Conversely, when the receptacle is heated by a heating unit,the crystal is, for an appreciable length of time, at a lowertemperature than the walls of the container, due to the poor conductingqualities of the air within the receptacle. These differences oftemperature between the crystal elcment and the receptacle have beenfound to affect, to a degree at least, the operating properties of thepiezo-electric crystal resonator. In accordance with the presentinvention, a temperature regulating system is provided which entirelyavoids such temperature differences.

It is also known that piezo-electric crystals in the state ofoscillation vibrate vigorously and tend to move from their normalposition between their electrodes. Inasmuch as the frequency ofoscillation of the crystal is affected by its position between itselectrodes it is a desideratum that for good frequency stability theposition of the crystal be fixed. This tendency of the crystal to moveWhile vibrating is appreciably diminished, if not entirely overcome, inaccordance with one feature of this invention which prevents movement ofthe crystal from its fixed position. This feature resides in theapparatus employed to hold the crystal in fixed relation with respect toits electrodes.

A further feature lies in the apparatus for actuating the heater controlrelay. This apparatus utilizes the fiow of fluids possessing electricaland heat conducting properties for opening and closing the circuit tothe control relay.

In accordance with this invention, the temperature of a piezo-electriccrystal resonator is controlled by utilizing one wall of a metallicblock as one of the crystal electrodes. A fluid, contained within theblock, is caused to control a circuit device by the variations intemperature of the crystal and block, in turn, controlling the flow ofcurrent in the apparatus.

One advantage of the present invention is that there is no substantialdifference in temperature between the piezo-electric crystal resonatorand the walls of the cell or block. This is due to the fact that one ofthe electrodes of the frequency control device forms an integral part ofthe cell wall.

Another advantage of this invention is that the temperature of thesystem can fall materially far below or rise far above the operatingtemperature at which the system is designed to function withoutdestroying the calibration of the control element.

Other objects, features and advantages will appear in a subsequentdetailed disclosure.

Referring to the drawing:

Fig. 1 illustrates diagrammatically a particular circuit embodiment ofthis invention for controlling the temperature of a piezo-electriccrystal resonator;

Fig. 2 is a plan view partly in the section of a crystal resonator andcell taken along the line 2-2 of Fig. 1. This view illustrates themanner in which the crystal is held firmly in position by the prongsextending inwardly from the crystal housing.

In Fig. 1 is shown a piezo-electric crystal resonatormounteddirectlyonametallic block I, which is filled with a nonelectricalconducting fluid 2. This fluid may be any suitable nonconducting fluidsuch as castor oil, kerosene and ether, which are herein mentioned onlyas being illustrative of any fluid which may be used. Metallic fins 3extend downwardly from one surface of the block I into the fluid 2. Alarge surface of contact is thus provided between the block and thefluid which tends to prevent any appreciable difference in temperaturebetween these two elements. For heating the unit a heater wire 4 isprovided which connects with a source of current supply. This heaterwire is supported by the metallic fins 3 and insulated therefrom. Theheating element or wire may comprise any means known to the art and isnot limited to the exact form shown in the drawing. In the use of theparticular emmeans of cock 6 and tube 5. Chamber 52 is provided with anopening 53 leading directly to the atmosphere. The purpose of thisopening will be described later. This chamber is filled with the fluid 2to the level H. Chamber 5| connected to chamber 52 by tubing is providedwith a heavy electrical conducting fluid such as mercury, which isadapted to complete an electrical circuit between metallic plates 9 andI5, extending through the glass walls, whenever the heavy fluid makescontact with both plates simultaneously. The level of the mercury beingindicated at 54 in chamber 5| and 55 in the chamber 50, a position whichis just slightly below the upper contact in chamber 5|. A relay circuitextends from metallic plates 9 and Ill to the box indicated at 4|.Circuit 5| may comprise any type of circuit known to the art such asshown in the drawing which is adapted, when electrical conducting pathacross plates 9 and I is closed, to open the source of electrical supplyconnected to the heater wire 4 and, whenever the circuit across theplates 9 and ID is opened, to again connect the source of current supplyto the heater element.

The cock 6 is adapted to connect the inside of block I directly withchambers 50 and 52 as illustrated in the drawing or when rotated 90degrees clockwise, to connect the inside of the block with chamber 55only.

The operation of the temperature control system will now be described.Assuming that it is desired to maintain the temperature of the crystalresonator and cell at 50 degrees C., the cock 6 will be set in theposition shown in the drawing by the operator. An electric current willflow through the heater wire 4 and will cause nonelectrical conductingfluid 2 to be heated, in turn heating block I. As fluid 2 expands, itwill flow through tubes and I2 into the glass chamber 52 causing thelevel I I of the fluid in this chamber to rise. The fluid 2 will notflow into the chamber 58 from block I at this time due to the balance ofpressure during this initial expansion. As

. soon as the temperature of the block has reached the desired value,which is in this particular embodiment degrees C., the operator willrotate the cock 6 clockwise 90 degrees, thus closing chamber 52 to theinside of block I and the cock will remain in this position. The storagespace in chambers 50, 5| and 52 maintains the calibration and obviatesthe necessity of again setting cock 6. Chamber 50 will now be the onlychamber communicating directly with block I through tube 5 and willreceive any further expansion in the fluid 2. The flow of the liquidinto chamber 58 from tube 5 will alter the mercury levels and thus forcethe mercury out of chamber 50 and into tube I3 to chamber 5|, causingthe mercury in chamber 5| to rise and make contact with metallic plate9. The mercury being already in contact with metallic plate I0 willcomplete a circuit to operate the relay apparatus in box 4|, which theblock, the temperature will now begin to fall,

this process will continue repeating itself. Due to the great heatstorage in the fluid 2, the actual temperature change required to turnthe heat on and off again is so small as to have a tween metallic plates9 and III as soon as the temperature of the fluid in block I begins tofall. The mercury will now be forced into chamber 55. At this time itshould be noted that the volumes of the chambers are such that mercurycannot be forced entirely out of chamber 5! nor can .3.

the fluid 2 be sucked entirely out of chamber and the volume of chamber52 is such that the level H of fluid 2 cannot drop below the top of themouth of tube I2 by a drop in block temperature due to power failure orsimilar causes. :-:-1

On the other hand, if for any reason, the control circuit in box 4|fails to function properly and the temperature of the block I continuesto rise above the operating temperature-4n this case 50 degrees C.thevolume of the mercury in 1.

chamber 55 is such that a reasonable factor of safetysay 10 degreesrise(60 degrees C.) will not cause fluid 2 to be forced past themercury,

thus destroying the calibration. Chamber 52 is made suiflciently largeso that there will not be any overflow through the opening 53 in the topof the chamber caused by an abnormal rise in temperature.

In actual practice there will always be a slight difference intemperature between block I and the fluid 2 due to the heat resistancebetween these two elements. This temperature will vary with the amountof heat which flows from the fluid 2 to the block I. temperature fall,the heat dissipated from block I will increase and the temperaturedifference between fluid 2 and block I will increase due to theincreased heat flow. Thus, there is a tendency for the temperature ofblock I to drop with a drop in atmospheric temperature. enecy is,however, compensated by the effect of the change in atmospherictemperature on the volume of fluid 2 in chamber 50 and the mercury inchambers 50 and 5|. This compensating action will now be described.

As the temperature of the atmosphere falls, the temperature of the fluidand mercury in chambers 50 and 5| also falls, causing the fluid tocontract. This contraction causes the mercury in chamber 5| to becomelowered, having the same effect as though the fluid inside block I wascooling and the volume decreasing. In order to have the mercury againmake contact with plate 9 the temperature of the fluid 2 within block Imust be raised an amount such that the corresponding expansion of thefluid in block I will be equal to the contraction of the fluid inchamber 50. This will cause an amount of heat to be supplied whichcompensates for the increased temperature difference between the fluidshould the atmospheric.

This tend- L 2 and block I. One method of obtaining the desired relationbetween the volume of the fluid in chamber 50 and the volume of thefluid in block I is to vary the amount of radiating surface betweenblock I and the atmosphere by using suitable heat insulators. A furthermethod of obtaining the desired relation which may be employed involveschanging the area of contact between fluid 2 and block I by changing thenumber or size of fins 3. In this manner the temperature of the crystalcell may be held at the 50 degrees C. level to within one hundredth ortwo hundredths of a degree C.

A particular feature which aids in maintaining the crystal cell at aconstant temperature is the raised boss on block I forming the lowerelectrode 22 of the cell. This boss may be plated with a specialconducting metal such as silver and is ground to a smooth finish.Secured to lower electrode 22 in such a manner that its temperature isalso regulated, is a metallic ring 33 forming part of the crystalholder. Located within this ring is another ring 34 for holding thecrystal in its proper position. This ring 34 is designed to fit tightlyagainst the inner surface of ring 33 and is held firmly in place by rods29 and 30. Two parallel prongs 52, 52 are provided on each side of ring34 and extend inwardly toward the center for holding the crystal 2| inplace.

These prongs may be cut oil to any desired length 1 for spacing theupper electrodes 23 and 24 the desired amount above electrode 22. Thesespacers may be provided with screws which fit into electrode 22. In thisembodiment the upper electrode is divided into two concentric electrodes23 and 24, which are mounted on a disk of insulated material 25 such asbakelite. These electrodes may either be screwed into the disk or if thedisk is made of a material such as Isolantite, the electrodes 23 and 24may be fused to it. The surfaces of these electrodes are ground veryaccurately to a true plane surface with the faces plated with a specialconducting metal such as silver. Disk 25 is designed to have a slightlysmaller diameter than the inner diameter of ring 33 with segments cut attwo points to permit insertion of rods 29 and 30.

This upper electrode assemblage is adapted to bear on rods 29 and 30 andto be held securely in place by the pressure of spring 3I. A pluralityof springs 32 pressing down upon the top of the assemblage are utilizedto force it against quartz spacers 26, 21 and 28. These springs may berotated out of the way if it is desired to remove the upper electrodeassemblage. Although one spring 32 is shown, it is to be understood thatthere may be as many such springs as are considered desirable. Terminals36, 31 and 38 provide electrical connection from the crystal cell toother parts of the system not shown.

Although the temperature control system has been described in connectionwith a piczo-electric \crystal resonator, it is to be understood thatthis form of temperature control is not limited in {scope thereto, butmay be employed for the control of the temperature of any other object.

What is claimed is:

1. A temperature regulating device having a container composedsubstantially of metal, a heating element within the body of saidcontainer, an external source of power for heating said element, atleast one of the walls of said container being in intimate thermalcontact with one of the electrodes of a crystal resonator, anonconducting fluid surroundin said heating element, said non-conductingfluid being adapted to expand and contract in accordance with variationsin temperature of said crystal resonator, an insulating containerlocated and supported outside said metallic container, said insulatingcontainer having three separate chambers which are in fluidcommunication with each other and also said metallic container, aconducting fluid retained within at least one chamber of said insulatingcontainer, the non-conducting fluid normally located within the othertwo chambers of said insulating container, means for controlling theflow of said fluids within said chambers, said second mentioned fluidbeing responsive to the actions of said first mentioned fluid forcontrolling the source of power supplied to said heating element.

2. A temperature regulating device having a container composedsubstantially of' metal, a heating element within the body of saidcontainer, an external source of power for heating said element, atleast one of the Walls of said container being in intimate thermalcontact with one of the electrodes of a crystal resonator, anon-conducting fluid surrounding said heating element, saidnon-conducting fluid being adapted to expand and contract in accordancewith variations in temperature of said crystal resonator, a conductingfluid retained within an insulating container and supported outside ofsaid metallic container by an upward extending communicating memberhaving a valve for controlling the flow of said fluids, said secondmentioned fluid being responsive to the actions of said first mentionedfluid for controlling the source of power supplied to said heatingelement.

3. A temperature regulating device having a container composedsubstantially of metal, a heating element within the body of saidcontainer, an external source of power for heating said element, atleast one of the walls of said container being in intimate thermalcontact with one of the electrodes of a crystal resonator, anon-conducting fluid surrounding said heating element, saidnon-conducting fluid being adapted to expand and contract in accordancewith variation in temperature of said crystal resonator, a conductingfluid retained within a plurality of insulating chambers and supportedoutside of said metallic container by an upward extending communicatingmember having means for controlling the flow of said fluids, said secondmentioned fluid being responsive to the actions of said first mentionedfluid for controlling the source of power supplied to said heatingelement.

4. A temperature regulating device having a container composedsubstantially of metal, a heating element within the body of saidcontainer, an external source of power for heating said element, atleast one of the walls of said container being in intimate thermalcontact with one of the electrodes of a crystal resonator, anon-conducting fluid surrounding said heating element, saidnon-conducting fluid being adapted to expand and contract in accordancewith variations in temperature of said crystal resonator, a conductingfluid retained within a plurality of insulating chambers, at least oneof said chambers having metallic contacts and supported outside saidmetallic container by an upward extending communicating member havingmeans for controlling the flow of said fluid, said second mentionedfluid being responsive to the actions of said first mentioned fluid andcooperating with said contacts for controlling the source of powersupplied to said heating element.

5. A temperature regulating device having a 'container composedsubstantially of metal, a heating element within the body of saidcontainer, an external source of power for heating said element, atleast one of the walls of said container being in intimate thermalcontact with one of the electrodes of a crystal resonator, anon-conducting fluid surrounding said heating element, saidnon-conducting fluid being adapted to expand and contract in accordancewith variations in temperature of said crystal resonator, a conductingfluid retained within a plurality of insulating chambers having upperand lower communicating members, at least one of said chambers havingmetallic contacts and supported outside said metallic container by anupward extending communicating member having means for controlling theflow of said fluids, said second mentioned fluid being responsive to theactions of said first mentioned fluid and cooperating with said contactsfor controlling the source of power supplied to said heating element.

6. A temperature regulating device having a container composedsubstantially of metal, a heating unit within said container, anexternal source of power for heating said unit, at least one of thewalls of said container being in direct thermal contact with anelectrode of a piezo-electric crystal resonator, said electrode locatedon a raised boss of a metallic hollow block having contained thereinsaid heating unit, a non-conducting fluid surrounding said heating unit,an insulating chamber on the top of said hollow block and adjacent saidboss, said insulating chamber having fluid communication with saidmetallic hollow block, a conducting fluid within said chamber, anexternal relay circuit connected with said heating unit, a pair ofelectrical contacts located in said chamber, so that when thenon-conducting fluid expands within the hollow block it will cause theconducting fluid in the chamber to rise so as to complete the said relaycircuit and cut ofi the current supply in said heating unit.

7. A temperature regulating device having a container composedsubstantially of metal, a heating element within the body of saidcontainer, an external source of power for heating said element, atleast one of the walls of said container being in intimate thermalcontact with one of the electrodes of a crystal resonator, said wallwhich is in intimate contact with said crystal resonator having aplurality of depending metallic fins, insulating means for supportingsaid heating element by said fins, a non-conducting fluid surroundingsaid heating element, said nonconducting fluid being adapted to expandand contract in accordance with variations in temperature of saidcrystal resonator, an insulating container located and supported outsidesaid metallic container, said insulating container having'three'separate chambers which are in fluid communication with eachother and also said metallic container, a conducting fluid retainedwithin at least one chamber of said insulating container, thenon-conducting fluid normally located Within the other two chambers ofsaid insulating container, means for controlling the flow of said fluidswithin said chambers, said second mentioned fluid being responsive tothe actions or" said first mentioned fluid for controlling the source ofpower supplied to said heating element.

LLOYD L. YOUNG. JAMES L; FINCH.

